The $250,000 ad buy in the states of the Democratic senators — who both face reelection in 2014 — is the first of a larger $750,000 campaign by the American Energy Alliance (AEA).

“If carbon tax supporters believe they are an unstoppable force, we want to let them know that they will meet an immovable object,” AEA spokesman Chris Warren told The Hill.

The Begich ad will run on TV in the Anchorage, Fairbanks and Juneau markets. The Hagan blitz is centered on radio markets across North Carolina.

The group said March votes from Begich and Hagan on measures attached to the nonbinding Senate Democratic budget plan amounted to support for a carbon tax.

Both senators voted against an amendment from Sen. Roy Blunt (R-Mo.) that would have blocked a carbon tax. The amendment got 53 votes but needed 60.

Begich also voted for an amendment from Sen. Sheldon Whitehouse (D-R.I.) that called for a “fee on carbon pollution,” which failed.

Begich's campaign, however, has recently said the Alaska Democrat opposes a carbon tax. Begich was facing pressure from the National Republican Senatorial Committee, which was spearheading a robocall effort denouncing Begich's support of a "radical" carbon tax.

Still, the AEA ad takes aim at Begich for the March vote, which used a Heritage Foundation analysis that said a carbon tax would cost the average family $2,000 annually.

"And Alaska's economy, where one-third of all jobs are related to energy development, will take a huge hit," the advertisement says.

Begich's campaign pushed back against the ad on Thursday.

It said the Whitehouse amendment wasn't a black-and-white vote on whether to directly tax carbon emissions — leading Susanne Fleek, Begich's campaign manager, to call the ad "misleading."

"Misleading ads like this one are just another reason Alaskans don't like Outsiders telling them what to do," Fleek said in a statement that referred to the billionaire Koch brothers, who are some of AEA's financial backers.

Hagan's campaign also weighed in on the ad, calling it "misleading" and asserting the North Carolina Democrat opposes a carbon tax.

"Unlike the special interest outsiders trying to distort her record, Senator Hagan is standing up for North Carolina families and our state's jobs each and every day," campaign spokeswoman Sadie Weiner told The Hill in an email.

The idea of a carbon tax has little political traction on Capitol Hill.

A majority of the Senate backed Blunt’s anti-carbon tax measure. And the GOP-controlled House already has approved legislation that would prevent a carbon tax.

The White House has also said it would not pursue a carbon tax.

Conservatives argue the tax would increase energy prices and burden the economy.

“A carbon tax isn't a tax on carbon, because carbon doesn't pay taxes. In reality, it's a tax on people who will pay for it every month in their utility bills, every week at the gas pump, and every day with increased tax burdens and shrinking discretionary income,” AEA President Thomas Pyle said in a statement.

Most carbon tax schemes, though, would return some of the revenue to residents to offset higher energy costs.

An idea backed by some conservative think tanks, and championed by former Rep. Bob Inglis (R-S.C.), would use the revenue to lower personal tax rates.